Seasonal pseudohyperkalaemia: no longer an issue?

Spurious hyperkalaemia is a well-recognized problem when reporting potassium results in samples originating from Primary Care. This is particularly relevant in laboratories serving large geographical areas where sample transport can cause significant delays in sample centrifugation. We have carried out a retrospective audit comparing serum potassium results on samples centrifuged at the general practice (GP) with those centrifuged on arrival at the clinical laboratory.

Potassium results were reviewed on serum samples received from 87 GPs in the Grampian region between August 2010 and March 2011. Potassium results were compared between samples centrifuged at the practice versus those centrifuged on arrival at the clinical laboratory.

In the period between November 2010 and February 2011, median monthly serum potassium results were significantly different between samples centrifuged at practices and those centrifuged on arrival at the laboratory. Median potassium concentrations were 10.2% higher in January 2011 (4.8 mmol/L; interquartile range [IQR]: 4.5-5.1) compared with August 2010 (4.3 mmol/L; IQR: 4.0-4.6). A similar trend in monthly median potassium concentrations was not evident in samples centrifuged at source over the same period.

The introduction of centrifuges into all GPs across NHS Grampian has significantly reduced the effect of seasonal variation in serum potassium results. There has also been a concurrent reduction in the number of cases of spurious hyperkalaemia. This exercise has significantly improved the overall quality of potassium results reported to Primary Care.